The invention is concerned with synchronising the multiplex lines which connect a time-division exchange to other time-division or electromechanical exchanges or to line concentrators connected to a number of subscribers. A time-division exchange transmits speech and non-speech signals using pulse code modulation. The signals are contained within the time slots of a frame carried by the multiplex lines. Each multiplex line connected to a time-division exchange provides a connection to an exchange or line concentrator with its own ("distant") clock. The time-division exchange has its own ("local") clock. As is well known, the distant and local clocks are not in phase, since they are not exactly synchronous. Multiplex lines are also subject to the phenomenon known as "jitter". Jitter is induced by the use of the digital transmission and involves spurious modulation of the times at which the pulses are centred. For this reason, before a time-division exchange is able to process data from another exchange or line concentrator, the incoming data in phase with the distant clock wd must be resynchronised with the local clock w.
Synchronising devices are already known in the art, in particular that described in the article "Groupement d'equipement de synchronisation du systeme de commutation temporelle Platon" by D FEUERSTEIN, J B JACOB, R RENOULIN and J GUEZOU in the review "Commutation et Electronique" No 34, July 1971. Such known devices are complex and do not totally eliminate jitter when present to any significant extent.